Starts, loses gas and running rough?

JASON JOHNSON

MEMBER
1999 GMC YUKON
5.7L
V8
4WD
AUTOMATIC
230,000 MILES

It I shutting off after it gets warm. I have replaced fuel pump cleaned tank, fuel pump, the wires harness, is new as well and lines all the way up to fuel rail checked for vacuum leaks as well and filter. The only codes I can get to throw are lean fuel bank 1 EGR valve is new same with TPS and IAC, and MAP sensor is new as well. New plugs and wires and cap and rotor, ignition coils are new as well and module. If you have hard time starting in wet conditions check the main wire that runs from ignition coil to rotor somehow moisture gets in there and messes, it up. I'm about to get a crankshaft sensor, and cam sensor plus a coolant temperature sensor for it as well. Could it be a worn distributor or timing, or do I need to have my wiring to fuel injectors checked or could it be the injectors? If I had the money, I'd replace all of them. But I don't and I'm worried it still would not fix it. This thing I. Great shape so no matter what I'm going to fix it even if I have to replace everything. My engine is just like the early GMC truck central layout.

5 Replies

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

The lean fuel mixture is likely caused by a vacuum leak. That could cause both of the issues you mentioned. What code was actually found?

If you haven't already, check to see if there are any leaks.

Here is a link that explains how to do it:

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

Also, you mentioned the EGR. Is there anything that could be causing it to stick open?

Let me know. Also, let me know what code was found and if there are any exhaust leaks. If you have a leak before the catalytic converters, that can show as a lean mixture causing the computer to work to adjust it. Let me know how it runs when the engine is first started.

Take care,

Joe

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Saturday, November 19th, 2022 AT 9:44 PM

JASON JOHNSON

MEMBER
5 POSTS

When it first started it runs great, even idling sounds fine drives great as well. When going down the road though it will just start slowing down like gas is shut off. If you hold it to the floor, you can maintain your speed a bit and then it just kicks in and is fine again but keeps happening after that on and off every few miles. The exact code I can't remember atm but it was for sensor 1 bank 1 lean and sensor 2 bank 1 lean right before the codes went permanent though it did show codes for high voltage on both of them sensors. Oh, and when I pulled my plugs almost all of them, even bank 2 side looked like signs of a lean mix. I tried to blow some smoke up brake booster hose and the end of hose that connects to intake had slight leak as well as the IAC which I had just replaced opened that up and o ring was defective so fixed that didn't see smoke from anywhere else. Assuming I need to redo this with a completely warm engine. If I remove the air intake while it's running it dies immediately when warm. After it has been driven and is warm its idle changes get a weird vibration there's one exhaust bolt on the donut stripped out so I will have to probably replace that stud but it's on passenger side. If it was the problem, you would think I would get bank 2 codes.

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Monday, November 21st, 2022 AT 12:27 PM

JASON JOHNSON

MEMBER
5 POSTS

My battery is in my other truck atm had to get one on the road, lol. Getting a new battery in the next day or so then I can get codes and data stream for it with my scanner. This may or may not be related but the neutral safety switch harness was damaged, and I changed that out. Brake booster check valve wasn't working right until I cleaned it up.

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Monday, November 21st, 2022 AT 12:48 PM

JASON JOHNSON

MEMBER
5 POSTS

And o2 sensors are new cats aren't plugged. I also found that the wires to neutral safety switch were damaged I replaced them awhile back.

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Monday, November 21st, 2022 AT 12:54 PM

JACOBANDNICKOLAS

MECHANIC
109,885 POSTS

Hi,

Are you getting a lean mixture on both banks? You indicated they were both lean and then said if it was the exhaust leak, you would be getting a bank 2 code.

Let me know. Also, if you do have a lean mixture on both sides, it's either a leak or a weak fuel pump. An exhaust leak pre-cat can cause it, but as you said, it would likely refer to that one side.

Let me know. Also, when you scan it again, let me know what the codes are.

Take care,

Joe